This application seeks support for a five-year study of learning processes in mentally retarded children. The focus will be on analysis of persistent discrimination learning problems that are frequently observed in this population. The overall goals of the program are to (a) increase basic understanding of why these problems occur and (b) devise effective solutions to them. The studies will focus on simple and conditional discrimination procedures like those used in special education settings. Particular emphasis will be placed on development and extension of highly promising procedures that have emerged from our recent research. The Specific Aims of the proposed program are to: (1) determine the relationship of certain subject and training variables to the persistence of undesired stimulus control in discrimination learning; (2) analyze variables that may be critical to the success of procedures that cull out desired stimulus control from a baseline that also includes undesired control; (3) determine whether failures of stimulus control transfer with "errorless" teaching procedures might be due to unmeasured competing stimulus control rather than to exclusive reliance on prompting stimuli during the transfer procedure; (4) examine the usefulness of novel procedures for evaluating stimulus-stimulus relations and generalized relational stimulus control; (5) time permitting, evaluate a possible relationship between subject and training variables and the degree to which mentally retarded individuals can discriminate stimuli correlated with different reinforcement densities and work requirements; and (6) to compare generalization results after training with either standard discrimination training procedures or those designed to minimize acquisition of unwanted stimulus control.